1. Field of the Invention
This invention relates to technology for preventing poor flotation performance due to oxidation of sulfide minerals in sulfide ore due to the work of bacteria when processing sulfide ore that is stored in a stockpile, and for preventing acidic wastewater that contains heavy metal components from being generated in the sulfide ore in a tailings dump site.
2. Description of the Related Art
In a non-ferrous metal mine, generally the mined sulfide ore is stored in an outdoor stockpile and quarried a fixed amount at a time, then processed using a method such as a flotation process. In the case where it is also necessary to mine low-grade sulfide ore, it is not reasonable from an economic standpoint to process it at the same time as high-grade sulfide ore, and so low-grade sulfide ore is stored separately in a special stockpile. This low-grade sulfide ore is then processed after mining of the high-grade sulfide ore has been completed, however, often it is left unattached for long periods of several years, and during that time, the sulfide minerals contained in the sulfide ore are oxidized and on oxidant film is formed on the surface formed due to the effects of bacteria in the sulfide ore such as iron oxidizing bacteria or sulfur oxidizing bacteria.
In the ore flotation process, a collector containing a hydrophobic group is caused to adhere to the surface of a certain sulfide mineral and caused to come to the surface, however, when the sulfide mineral is oxidized, the adsorption rate of the collecting agent decreases, such that the recovery rate of the target metal also decreases. In this case, countermeasures are taken such as adding a sulfidizing agent like sodium hydrosulfide and sulfidizing the surface of that sulfide mineral again, or making the particle size of the crushed ores more fine, however, the cost of the sulfidizing agent increases, and there is a need for certain processes and equipment to take such countermeasures, so the economic burden as well as other burdens become large.
Also, ultra-low-grade sulfide ore is not processed, but stored at a dumping site as tailings. The sulfide minerals such as iron pyrite that are contained in the dumped sulfide ore are exposed to and soaked in seepage water, and when oxidized by the oxidizing action of the bacteria in the sulfide ore, sulfuric acid is produced, and acidic waste water containing a heavy metal component is generated. This kind of phenomenon widely occurs in stockpiles or tailing dumpsites of sulfide ore, or in polluted or contaminated soil containing the same sulfide minerals, so neutralization and heavy metal sedimentation and separation is performed using wastewater treatment equipment.
A method of using lime to remove heavy metals as a hydroxide is widely used for processing this kind of acidic wastewater. Also, an iron co-precipitation method as disclosed in Japanese Unexamined Patent Publication No. H10-235375 or Japanese Unexamined Patent Publication No. H10-249362 is often performed. However, there is a problem in that these methods must be continued as long as acidic wastewater occurs, and reagent costs and maintenance costs of the equipment pose an economic burden.
Moreover, in methods disclosed in Japanese Unexamined Patent Publication No. H8-164399 and Japanese Unexamined Patent Publication No. H10-202300, efficiency of the process is improved by using iron oxidizing bacteria to oxidize the iron in the wastewater, however, maintenance of the equipment is still necessary, so the burden is large.
As a method for suppressing oxidation of the sulfide minerals themselves, there is a method of obtaining an anti-bacterial effect by causing a thickening agent to adhere to the surface of metal powder or metal-compound powder that is soluble in sulfuric acid, for example, there is a method disclosed in Japanese Unexamined Patent Publication No. H8-268823, however, it is difficult to perform this process uniformly and inexpensively for a large quantity of tailings or contaminated soil.